Lean limit internal combustion engine roughness control system

ABSTRACT

A closed loop fuel control mechanism for controlling the air fuel mixture delivered to an internal combustion engine so as to regulate the roughness of the engine at a predetermined level. The control system receives as input signal a signal indicative of the engine roughness and processes this signal to generate an output control signal for controlling the fuel delivery mechanism of the internal combustion engine to operate that engine at the leanest possible air/fuel mixture ratio compatible with a predetermined level of engine roughness.

a 7i i United States tent 1 1 1111 3,789,816

Taplin et a1. Feb. 5, 1974 [54] LEAN LIMIT INTERNAL COMBUSTHON 2,982,2765/1961 Zechnall et a1 123/32 EA X ENGINE ROUGHNESS CONOL SYSTEM gfiggggg13x32 fi ls! 1 13 g D a un ere... [75] In e 0 10 Llvoma; W111i!3,338,221 8/1967 $611611 123/119 R x Settz; Chain Keung Leung, both of3,483,851 12/1969 Reichardt 123/119 R Farmington, all of Mich. [73]Assignee: The Bendix Corporation, Southfield, Primary ExaminerwendellBums Mi h Assistant Examiner-Tony Argenbright [22] File M 29 1973Attorney, Agent, or FirmGerald K. Flagg [21] Appl. No.: 346,240 [57]ABSTRACT [52] Us. Chm 123/119 R 123/32 AE, 123/32 EA, A closed loop fuelcontrol mechamstn for controllmg 123/102 123/106 123/139 AW 123/198 Rthe an fuel mixture delivered to an internal combus- [51 Int. c1. F02115/00, F0211] 51/00, F02m 57/00 3% 3 i of [58] Field 61seam11...123/119R, 139 AW, 198 R, w W e e 9?" [0 eye em F 123/102 106 32 AB 32 EA 60/3909 ce1ves as mput slgnal a signal 1nd1cat1ve of the engine roughness andprocesses this signal to generate an output control signal forcontrolling the fuel delivery [56] References Cited mechanism of theinternal combustion engine to oper- UNITED STATES PATENTS ate thatengine at the leanest possible air/fuel mixture 2 670 724 3 1954 Reggio60/D1G. 6 ratio compatible with a predetermined level of engine2Zs42110s 7/1958 Sanders... 123 102 roughness 2,911,966 11/1959 Pnbble123/119 R 15 Ciaims, 5 Drawing Figures ROAD LOAD SIMULATOR FILTER aDIFFERENTIATOR /,W

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COMPAR ATOR 2 d ff SHEET 1 0F 2 AA: INTEGRATOR CONTROLLER PATENIEU 5 4ENGINE I DYNAMOMET ER EMISSIONS ANALYZ ERS ROAD LOAD SIMULATOR LOW PASSFILTER THRESHOLD i POT COMPARATOR PATENTED FEB 5 974 SHEEI 2 0F 2 LEANLIMIT INTERNAL COMBUSTION ENGINE ROUGHNESS CONTROL SYSTEM The presentinvention relates to closed loop engine controls in general and inparticular to closed loop engine controls of the type that control theair fuel mixture delivered to an internal combustion engine so as toregulate engine roughness at an acceptable level.

Closed loop control systems for controlling a parameter of an internalcombustion engine are well known in the art. For example the Pat. toDraper and Lee No. 2,628,606 and, the paper Principles of OptimizingControl Systems and An Application to the Internal Combustion Engine, byC. S. Draper and Y. P. Li, published Sept. 1951 by the American Societyof Mechanical Engineers both disclosed the use of a closed loop controlsystem, also known as an extremum or optimizing system, for oscillatingthe air and/or fuel flow to an internal combustion engine. Using theeffects of such dithering the optimizing system controls the engine soas to seek out and operate at its optimum power or most economical fuelconsumption point in spite of any reasonable change of output level orenvironmental operating conditions. Such optimizing systems, moreover,inherently effect some reduction in the formation of certain exhaust gasconstituents since the air/fuel mixture producing the optimum power ison the lean side of the stoichiometric air/fuel ratio and sinceincreasing leanness is known to reduce the formation of suchconstituents as carbon monoxide, hydrocarbons, and to some degreenitrous oxides.

However, the power optimization technique has not been incorporated inmass produced internal combustion engines and therefore the reduction information of certain emissions that might have been realized thereby hasheretofore not been obtained. Moreover such commercial adoption of thetechnique would be hindered by a combination of factors including thefollowing. The primary factor is that such optimizing systems are notonly effectual at idle and wide open throttle, two entirely normal modesof operation whereformation of emissions must nevertheless becontrolled, but also must be cut out or disconnected when the leannessof the air/fuel mixture causes the engine to start to misfire. Anotherfactor is that this technique does not control the power outputdirectly, nor for that matter does the technique require even themeasurement of the magnitude of the power output. Instead, momentarypower changes are effected only indirectly and then through atime-and-phase lag susceptible system. Thus, after dithering apower-affecting parameter only the positive or negative sense and notthe magnitude of they resulting power change is determined. As anotherfactor affecting its adoption, the optimizing technique requires thedithering of parameters that mightotherwise not be dithered and therebyintroduces undesirable performance consequences related to just suchdithering. A further factor is that the technique re quires thegeneration, synchronization, and comparison of the dithered parameterwith its effects and therefore incurs not only the cost andserviceability penalties associated with the extra equipment but alsothe effects of errors inherent in the equipment. Moreover these stepsare subject to phase and time delay errors beand being further subjectto the errors in the detection thereof.

Moreover, even if the theoretical benefits of the use of optimizationtechnique for effecting some reduction in the formation of emissionscould be realized commercially, the power optimization techniqueactually prevents operating the engine as lean as possible so as toreduce emissions as much as possible. In view of the aforementionedoperational limit imposed by the occurrence of occasional misfires, thepower is maximized at an air/fuel ratio which is substantially richerthan the leanest of air/fuel ratio at which the engine could be operatedbefore the resulting leanness induced engine roughness causes vehicledriveability to become unacceptable.

Not only has this relationship between the leanness of the air/fuelmixture and engine roughness long been known but also the contributionto unacceptable driveability due to operation of the engine at its leanlimit has been measured, for example, by measuring cylinder pressurevariations or by measuring fore and aft linear motion of the vehiclebody, the latter measurements being described in the paper MeasuringVehicie Driveability by R. L. Everett, published as Paper No. 710137 forthe Jan. ll-l5, 1971 Conference of the Society of Automotive Engineers.The knowledge of the effect of leanness on vehicle driveability and themeans for measuring it not withstanding, the magnitude of vehicledriveability has heretofore not been controlled as the controlledparameter of a closed loop engine control system. Moreover, rather thanattempting to continuously and always maintain engine operation right atthe leanest air/fuel ratio possible, the prior art systems have usedthis limit only to disable themselves or effect engine operation at asafe margin from it.

It is desirable to be able to continuously control the formation ofcertain undesirable engine emissions during all modes of engineoperation and not during just certain modes and not during other normaloperating modes. It is also desirable to control the formation ofundesirable exhaust gas constituents in a more direct and lesscircuitous manner than with the power optimization technique and withoutincurring the equipment, error, and emission penalties associatedtherewith. It is also desirable to avoid the steps of generating,synchronizing, and comparing dither effects required by the poweroptimization technique by controlling the magnitude and not the sense ofa parameter related to engine performance. It is also desirable tocontrol the formation of certain exhaust gas constituents by controllinga clearly measurable parameter, the magnitude of which not onlyindicates actual engine performance and yet is also adjustable to permittrade-off between vehicle driveability and emission control.

It is therefore a prominent object of the present invention to provide anew and improved closed loop control system for reducing the formationof certain exhaust gas constituents of an internal combustion engine.

It is another primary object of the present invention to provide aclosed loop control system for regulating engine roughness.

It is a further object of the present invention to provide a closed loopair/fuel control system responsive to the magnitude of engine roughnessso as to maintain as lean an air fuel mixture as possible withoutexceeding a predetermined level of roughness.

It is another primary object of the present invention to provide aclosed loop control system for controlling the leanness of the air/fuelmixture delivered to an internal combustion engine so as to regulateengine operation at the threshold of unacceptable engine roughness.

It is a further object of the present invention to provide a closed loopcontrol system for sensing and regulating the magnitude of engineroughness. And it is another object of the present invention to providea closed loop engine control system of the foregoing type wherein themagnitude of engine roughness is determined by sensing anddifferentiating the speed changes of a rotatable engine member.

Furthermore, recognizing that the magnitude of engine roughness affectsvehicle driveability oppositely from the leanness-influenced formationof certain exhaust emissions, the present invention as another of itsobjects provides a closed loop control system for controlling engineroughness at a magnitude which is selected to effect a trade-off betweenvehicle driveability and the formation of such emissions.

As is also known, for the purposes of both vehicle performance andemissions control, to deliver the desired quantity of fuel to the engineduring certain modes of engine operation including certain drivercommanded engine performance changes requires that the fuel controlschedule be changed from that effected during steady state operation. Itis therefore another object ofthe present invention to provide a closedloop fuel control system that normally maintains as lean as air fuel aspossible so as to just follow the threshold of unacceptable engineroughness during steady state operation and that permits a differentcontrol of air fuel ratio to be effected in the presence of other modesof operation.

Furthermore, recognizing that certain driver commanded performancechanges contribute low frequency components of engine roughness, thepresent invention as another object provides a closed loop enginecontrol system that includes low frequency responsive apparatus formodifying the normal operation of the control system in accordance withlow frequency components of engine roughness. It is another object ofthe present invention to provide a closed loop engine control system ofthe foregoing type for normally maintaining the air fuel mixture as leanas possible so as to normally maintain the magnitude of engine roughnessbelow a first predetermined level, the low frequency responsiveapparatus preventing such normal operation of the control system whenthe magnitude of the low frequency components of engine roughness exceeda second predetermined level.

In accordance with the control system of the present invention, atachometer suitably coupled to a crankshaft driven member of an internalcombustion engine senses the high frequency speed changes thereofresulting from lean air fuel mixtures as well as low frequency speedchanges resulting from driver commanded engine performance changes. Thespeed signal developed by the tachometer is attenuated by a filter topass only the frequencies of interest and is then differentiated by adifferentiator to provide a raw roughness signal varying with aderivative of the speed signal. This raw roughness signal is full waverectified by a full wave rectifier and is thereafter compared by acomparator with a roughness threshold reference, the magnitude of whichis selected to correspond with a level of acceptable vehicledriveability. The output of the comparator is applied to an integratorwhich produces an increasing output when the engine roughness is belowthe acceptable driveability level and a decreasing output when theroughness is above this level. The output of the integrator causes anelectronic fuel injection system to vary the duration of the fuelinjection period so as to increase the leanness of the air fuel mixtureas long as the engine roughness is below the acceptable level and todecrease the leanness when the roughness momentarily exceeds this level,the net effect of such leanness control being to regulate the roughnessat this level.

These and other objects and features of the present invention willbecome more apparent from the following description taken in conjunctionwith the following Figures wherein:

F IG. 1 is an illustration partially in block diagram and partially inschematic of a closed loop internal combustion engine control system forcontrolling the air/fuel ratio so as to regulate the roughness of engineoperation;

FIG. 2 is a view partially in schematic and partially in cross-sectionof a fragmentary portion of fuel delivery apparatus of the closed loopinternal combustion engine control system of FIG. 1;

FIG. 3 is a block diagram representation of a portion of the closed loopinternal combustion engine control system of FIG. I modified by asub-loop for modifying the control of the leanness of the air/fuel ratioin the presence of certain-driver commanded performance changes;

FIG. 4 is an electrical schematic of the closed loop internal combustionengine control system of FIG. I as modified by a sub-loop similar tothat shown in FIG. 3; and

FIG. 5 is an electrical schematic of an alternative embodiment of theclosed loop internal combustion engine control systems in FIGS. 3 and 4.

With reference now to FIG. 1, there is shown an intermittently firingspark ignition internal'combustion engine 10 which is conventionalexcept that air and fuel are delivered thereto in a ratio controllableby a closed loop control system 12 so as to regulate the roughness ofengine operation. In the presently preferred embodiment, control system12 is operative to reduce the percentage of concentration of certainexhaust gas constituents in the combustion products of the engine 10 bybiasing the air/fuel ratio towards an engine performance related leanlimit as long as engine roughness is below a predetermined magnitudeand, when the roughness just exceeds the predetermined magnitude, todecrease the air/fuel ratio to decrease the roughness. In view of thispresently preferred embodiment, control system 12 is hereinafter termedlean limit loop 12 and is shown in a laboratory emission testingenvironment.

Thus, as illustrated in FIG. 1 a branch of the engine exhaust system 14of the engine 10 upstream of the muffler 16 thereof is shown connectedto emission analyzing apparatus 18 through a valve 20, and the outputshaft 22 of the engine transmission 23 is shown connected by a shaft 24and a torque cell 26 to an engine dynamometer 28. Engine dynamometer 28is responsive to commands provided by a suitable road load simulator 30such as a computer responsive to torque signals provided by torque cell26 and brake signals provided by a driver control 32. Driver control 32is connected electrically and/or mechanically to control a suitable airconsumption control device 34 in the form of throttle plates (not shown)mounted on a throttle shaft in the engine air induction passageintermediate an air intake end 36 thereof and an engine outlet endthereof.

Engine further comprises fuel delivery means 40 operable to control thedelivery of fuel flow so as to maintain a desired relationship to theair flow. As may be better understood in conjunction with FIG. 2, fueldelivery means 40 in the presently preferred embodiment comprises anelectronically controlled fuel injection system including anelectromagnetically operated fuel injector valve 42 mounted in theengine intake manifold 44 upstream therein of an engine intake valve 46(shown open) and operative to control the injection of fuel therethroughinto an engine combustion chamber 48, a pump 50 being provided to pumpthe fuel to injector valve 42 from a suitable fuel supply 52 through afuel rail and return conduit 54 having a flow restriction 55 therein.

The injector valve 42 is electrically connected by a conductor 56 to afuel delivery controller 60, hereinafter termed air fuel controller, ofthe type known in the art for controlling the length of the fuelinjection period by using one or more engine dependent parameters toeither vary the point at which such injection period commences and/or tovary the point at which such injection period terminates. Air fuelcontroller 60 in the presently preferred embodiment comprises a suitablepulse train generating device which may be of a type disclosed incommonly assigned and co-pending U.S. Pat. application Ser. No. 101,896filed on Dec. 28, 1970 issued as Pat. 3,734,068 on May 22, 1973 in thename of Junuthula N. Reddy and entitled Fuel Injection Control System,hereby expressly incorporated herein by reference.

As described in further detail the indicated Reddy application, fueldelivery controller 60 generates a pulse train of specially shapedvoltage vs. time signals, each pulse having a specially shaped beginningportion for determining the commencement of each injection period inaccordance with engine speed and a constantsloped ramp portion forterminating each injection pulse when the ramp portion intercepts apredetermined reference level related to air flow. To receive suchair-flow and speed-dependent intelligence, the air fuel controller 60 isconnected by a conductor 62 to a sensor 64 for sensing the air flow or aparameter related thereto such as the manifold air pressure and is alsoconnected by a conductor 66 to a speed sensor 68, speed sensor 68 in thepresently preferred embodiment comprising a 60 toothed tachometer wheelsuitably coupled to a suitable crankshaft driven member (not shown) ofengine 10, such as a flywheel, ring gear, or pulley thereof. Using theengine speed and air flow intelligence thus provided, air fuelcontroller 60 operates to modify the duration of the pulse injectionperiod so as to maintain a desired relationship between the air flow andthe fuel flow, such desired relationship varying from an air fuel ratioas low as 9 to 1 during cold engine starting conditions to slightlyabove the stoichiometric ratio of about 14.8 to l on completion ofengine warm up.

In accordance with the present invention the lean limit loop 12generates and applies to air fuel controller an air/fuel ratio changecommand that normally decreases the fuel injection period so as toincrease the air/fuel ratio until such ratio is biased to a limit solean that the engine just begins to run rough. The lean limit loop 12responds to this incipient roughness by momentarily decreasing theair/fuel change command and thereby enriching the air/fuel ratio, suchchange command increasing the fuel injection period by causing the rampof the controller generated pulse train to intercept the referencevoltage later, as might be effected either by decreasing the slope ofthe ramp portion and- /or by raising the reference voltage.

To thus continuously control the air/fuel ratio to in effect maintain itat its lean limit, lean limit loop 12 detects an engine parametervarying with the air/fuel ratio and then momentarily modifies theair/fuel ratio so as to control the engine parameter. One such parameteris engine speed since, as the air fuel mixture momentarily becomes toolean or too rich relative to the stoichiometric ratio, the powergenerated by different cylinders of the engine momentarily becomesuneven or rough, thereby causing the torque delivered by the piston tothe engine crankshaft to be correspondingly uneven or rough and therebycausing the crankshaft to momentarily accelerate or decelerate inaccordance with the uneven torque. Terming generically as engineroughness all such momentary power differences, torque changes,accelerations and decelerations, or the speed changes, the lean limitloop 12 of the present invention provide apparatus operative to detectsuch roughness and to modify the air/fuel ratio so as to maintain theroughness below a predetermined magnitude.

A roughness sensor suitable for use by the lean limit loop 12 is of atype described in greater detail in a copending and commonly assignedU.S. Pat. application Ser. No. 249,440 filed on Apr. 24, 1972, in thename of Taplin et a]. and entitled Surge Sensory Apparatus For A PrimeMover, such application being hereby expressly incorporated herein byreference. Briefly, such roughness sensor comprises a filter anddifferentiator 70 that receives a speed signal from the tachometer 68,attenuates frequencies outside a desired band of frequencies anddifferentiates the remaining nonattenuated speed signal to generate aderivative signal varying with at least the first derivative of thespeed signal. To permit the beneficial use of both the accelerationinformation and the deceleration information contained in thisderivative signal and also to condition this derivative signal forcomparison with a roughness reference signal, the output of thedifferentiator is applied by a conductor 72 to a full wave rectifier 74and therefrom to a comparator 76. A suitable source of adjustablereference voltage in the form of a potentiometer 78 is connected tocomparator 76 to provide a roughness threshold reference thereto.Comparator 76, in the presently preferred embodiment, produces acomparison signal of one polarity when the rectified roughness signal isless than the roughness threshold reference and of the opposite polaritywhen the rectified roughness signal is greater than the roughnessthreshold reference, such comparison signals being communicated by acomparison signal conductor 80 to an integrator 82. Integrator 82generates an A/F change command applied to air/fuel controller 60causing the controller to either continually shorten the period of thefuel injection pulse and thereby increase the air/fuel ratio towards alean limit as long as the output of com-- parator 76 is of the firstpolarity or to otherwise increase the period of the injection pulse todecrease the air/fuel ratio away from its lean limit as long as theoutput of comparator 76 is of the other polarity.

The magnitude of the threshold reference provided by potentiometer 78 isselected to correspond with a level of engine roughness at which theair/fuel mixture is made as lean as possible to the point that theformation of such exhaust gas constituents as HC and CO is minimizedwithout the driveability of the particular vehicle being unacceptable.To effect this trade-off between vehicle driveability and emissioncontrol the setting of the roughness threshold may vary from one engineapplication to another. For example, the roughness threshold may be setto tolerate engine speed changes as high as 12 r.p.m., as might be setfor engines driving hydraulically-coupled transmissions thathydraulically attenuate some of the roughness, or substantially lowerspeed changes, as might be set for engines driving clutch-coupledtransmission that transmit the engine roughness relatively unattenuated,the former setting normally producing fewer emissions under comparableoperating conditions than the latter.

As may be better understood with the reference to FIG. 3, a lean limitmodification sub-loop in the form of a cut-out loop 84 is providedshould it be desirable to modify the operation of limit loop 12 duringcertain conditions or modes of engine operation as, for example, toinhibit the fuel enrichment that would otherwise result from lowfrequency engine accelerations and decelerations associated with drivercommanded changes in vehicle performance. Such low frequency roughnesssignals while they are attenuated with respect to the roughness signalspassed unattenuated by filter and differentiator 70 to full waverectifier 74 nevertheless could still be of sufficient magnitude whendifferentiated and rectified to cause the rectified output of rectifier74 to exceed the roughness threshold. While in some applications of thelean limit loop 12 it may be desirable to use this extra component ofroughness information to enrich the air/fuel ratio during accelerationor conversely to lean out the mixture during deceleration, in thepresently preferred embodiment it is desired to control the leanness ofair/fuel mixture in accordance with just the roughness caused by theleanness of the mixture and not by components of roughness induced bydriver commanded accelerations or decelerations.

To effect such inhibiting of the operation of lean limit loop 12 underthese circumstances, cut-out loop 84 is connected in parallel around thefull wave rectifier 74 and comparator 76 oflean limit loop 12 at pointsdesignated A and B on conductors 72 and 80 thereof. Cutout loop 84comprises a low pass filter 90 connected in series with a full waverectifier 92, a comparator 94, a relay 98 and a switch S1, switch S1being inserted between comparator 76 and integrator 82 of the main leanlimit loop 12. Low pass filter 90 attentuates higher frequencycomponents of the roughness signal previously passed unattenuated byfilter'and differentiator 70 and passes without further attenuation thepreviously attenuated low frequency components of the roughness signalto full wave rectifier 92. Comparator 94 compares the rectified lowfrequency roughness signal provided by rectifier 92 with the lowfrequency roughness threshold signal provided by an adjustable source ofreference voltage 96, the magnitude of which is selected so as to permitcut-out loop 84 to modify the operation of main loop 12 only in thepresence of more than nominal driver commanded performance changes. Whenthe magnitudes of such performance changes are more than nominal,comparator 94 provides command signal to relay 98 causing switch S1 toopen the connection between comparator 76 and integrator 82 therebyinhibiting the normal operation lean limit loop until the effects ofsuch more than nominal changes have subsided.

As may be better understood with reference to FIG. 4, filter anddifferentiator comprises three filter stages comprisingresistor-capacitor combinations Rl-Cl, R2-C2, and R3-C3, in combinationwith a differentiator comprising operational amplifier A1, feedbackresistor R3, and capacitor C2. As described in greater detail in theabove-referenced Taplin et al. U.S. Pat. application Ser. No. 249,440,the three filter stages have a common frequency break at about 20radians per second on the log gain vs. log frequency plot and each suchstage constitutes a lag type network having a transfer functioncharacterized by l/(rs 1). More over, the differentiator has a lead typetransfer function characterized by TS so that the signal on conductor 72at the output of amplifier Al varies with the first derivative, in thiscase the acceleration or deceleration, of the speed signal appliedthrough differentiator input terminal Tl.

Full wave rectifier 74 comprises an operational amplifier A2 havinginverting and noninverting input terminals respectively connectedthrough oppositely polled rectifier diodes D1 and D2 to the output ofdifferentiator 70. With the anode of diode D1 connected through aresistor R4 to the inverting input terminal of amplifier A2, onlynegative signals are communicated thereto to produce only positivesignals at the output thereof. Similarly, with the cathode of diode D2referenced to ground through resistor R5 and connected to thenoninverting input terminal of amplifier A2, only positive signals arecommunicated thereto to also produce just positive signals at the outputthereof.

Threshold comparator 76 comprises an operational amplifier A3, theinverting input terminal of which is connected to both the output ofrectifier amplifier A2 through resistor R7 and to the output terminal ofamplifier A3 through a pair of series-connected oppositely-polled Zenerdiodes D3 and D4. A roughness threshold reference voltage is provided byan adjustable potentiometer 78, the fixed element R10 of which isconnected between a suitable negative supply and ground and the wiperarm of which is connected to the inverting input terminal of A3 throughresistor R8. The noninverting input terminal of amplifier A3 is groundso that a slightly negative voltage is provided at the inverting inputterminal when the output of a full wave rectifier 74 is less than thereference voltage provided by the potentiometer. With this slightlynegative input to the inverting input terminal of amplifier A3, theoutput thereof on conductor 80 is a positive value determined by thebreakdown voltage of Zener D4. As the output of full wave rectifier 74increases to exceed the output provided by the threshold reference 78,the voltage at the inverting input terminal of amplifier A3 comesslightly positive to cause amplifier A3 to rapidly produce a negativeoutput, the step change transition from the positive to the negativeoutput being assured by the high gain of amplifier A3 and the level ofthis output being determined by the breakdown voltage of Zener D3.

The output of comparator 76 on conductor 80 is applied to integrator 82via resistor R11, normally closed and sub-loop-operated loop-cutoutswitch S1, and a normally closed manually operated air/fuel presetswitch S2, the purpose and operation of switches S1 and S2 beingdisclosed in further detail below in conjunction with loop cut-outcircuit 84 and preset air fuel command circuit 86 respectively.Integrator 82 is of conventional design, here comprising an operationalamplifier A4 the inverting input terminal of which is coupled to theoutput terminal T2 by a capacitor C4 and the noninverting input terminalof which is grounded. During normal operation of lean limit loop 12switches S1 and S2 are both closed to communicate the output ofcomparator 74 to the integrator 82. Then, if the rectified roughnesssignal provided by full wave rectifier 74 is less than the roughnessthreshold reference provided by potentiometer 78, the resulting negativeoutput of comparator 76 causes the output of integrator 82 to increasepositively at a positive rate determined by the magnitudes of resistorR11 and capacitor C4. This output is coupled directly to air/fuelcontroller 60 and is suitably processed thereby to increase the air/fuelratio by shortening the fuel injection period in a suitable mannersimilar to that as has been heretofore generally described. Conversely,if the rectified roughness signal is greater than the roughnessthreshold, the resulting positive input to integrator 82 causes theoutput thereof to decrease negatively at a negative rate to decrease theair/fuel ratio.

Even though the air/fuel ratio is normally controlled primarily by theoutput of the integrator 82, it may nevertheless be desirable to effecta predetermined air/fuel ratio during certain periods or conditions ofoperation. in the present embodiment, if comparator 76 were connected tointegrator 82 with the engine off, the air/fuel ratio might be renderedtoo lean to permit subsequent starting. Therefore, to provide a pre-setair/fuel ratio suitable for engine starting operations lean limit loop12 further comprises an air/fuel pre-set circuit 86 that is operative todisconnect the input of integrator 82 from the output of comparator 76and connect it instead to a known reference. A/F pre-set circuit 86comprises the A/F pre-set switch S2 connected between S1 and theinverting input terminal of amplifier A4, voltage dividing resistors R12and R14 connected in series between the output terminal T2 of amplifierA4 and a resistor R13 connected between a suitable negative supply andground, and a conductor 88 connecting the node between resistors R1 1and R12 to one contact of switch S2. With A/F pre-set switch S2 in thestart-up position connecting conductor 88 to the inverting inputterminal, the output of amplifier A4 is stabilized at a positive valuereflective of the slightly negative voltage at the node betweenresistors R12 and R14. After the engine has been successfully started,A/F pre-set switch S2 is switched to the run position connecting theinverting input terminal to the output of comparator 76 instead of theA/F pre-set command circuit.

To open cutout switch S1 and thereby disable lean limit loop 12 when themagnitude of low frequency roughness signals exceeds a low frequencyroughness threshold, the output of differentiator and filter 70 onconductor 72 is applied to a conventional low pass filter comprising aresistor R15 in series with a capacitor C5, capacitor C5 also beingconnected in parallel with a resistor R16 between the inverting inputterminal and the output terminal of an operational amplifier A5 toprovide a unity gain therethrough.

The output of low pass filter 90 is applied on conductor 91 to the inputof both a half wave rectifier stage 92' and the comparator stage 94'. Aswill be described more fully shortly, these stages cooperate to performexactly the same functions as the full wave rectifier 74 and thecomparator 76 of the primary lean limit loop 12 but provide betterlinearity between input and output signals of small magnitudes byeliminating diodes comparable to diodes D1 and D2 in the input path toamplifier A2 and thereby avoiding the attenuation otherwise introducedby the forward drop of such diodes. And this in turn is permitted byconnecting the output of the low pass filter 90 to both the half waverectifier stage 92' and the comparator stage 94' rather than to just thefull wave rectifier stage 74 as in the case of .the primary lean limitloop 12.

To obtain this result the output of low pass filter 90 is communicatedby conductor 91 and resistors R17 and R18 respectively to the invertinginput terminals of operational amplifiers A6 and A7, amplifiers A6 andA7 having their noninverting input terminals suitably grounded andcomprising portions of the half wave rectifier stage 92 and thecomparator stage 94 respectively. The output of amplifier A6 isconnected to both the anode and the cathode respectively of diodes D5and D6, the cathode and anode of which are respectively coupled to theinverting input terminal of amplifier A6 via resistors R20 and R21respectively. With such connections, a positive output from low passfilter 90 causes a negative voltage at the output terminal of amplifierA6. This causes current to flow from the input to the output terminal ofamplifier A6 through resistor R21 and diode D6 so that the resultingvoltage at the node 95 between the anode of diode D6 and resistor R21varies inversely with the product of the positive input voltage timesthe ratio of forward drop of diode D6 divided by the amplifier gain. Onthe other hand a negative output from low pass filter 90 back biasesdiode D6 so that it does not conduct with the result that the voltage atnode 95 is virtually zero due to the feedback from the output to theinput of the amplifier through diode D5 and resistor R20.

The voltage at node 95 is communicated to the inverting input terminalof amplifier A7 through a resistor R22 which, in the presentapplication, is selected to have half the magnitude of resistor R18.With this relationship between the resistances of resistors R18 and R22,any negative voltage communicated from node 95 to the inverting inputterminal of amplifier A7 is attenuated only half as much as a positivevoltage communicated across resistor R18 from the output of low passfilter 90. Thus, considering just the inputs to amplifier A7 providedthrough resistors R18 and R22, the ratio therebetween causes a positiveoutput of one volt from low pass filter 96 to result in a net negativeinput of one volt to amplifier A7 since the positive voltage createdacross resistor R18 is only half of the two volt negative potentialcreated through resistor R22. To this extent, the positive output of lowpass filter 90 is therefore at least half way rectified. Conversely, anegative output of 1 volt from low pass filter 90 also causes a negativeinput to amplifier A7, this negative input being created throughresistor R18 alone since, as has been hereinabove been indicated,voltage at node 95 is virtually ground under these conditions. Moreover,to the extent that inputto amplifier A7 is negative for both positiveand negative outputs from low pass filter 90, such output is thereforefully rectified.

Also comprising a portion of comparator stage 92 is a suitableadjustable voltage reference in the form of a potentiometer 96, thefixed resistor R23 of which is connected between the suitable positivesupply and ground and the wiper arm of which is connected to theinverting input terminal of amplifier A7 through a resistor R24. Toactivate relay circuit 98 and thereby cause cut-out switch S1 to open orcut out the main lean limit loop 12 when the low frequency roughnessreference established by potentiometer 96 is exceeded by the full waverectified output of low pass filter 90, the inverting input terminal ofamplifier A7 is also connected by a forward polled Zener diode to theoutput thereof and therefrom through a resistor R25 to the base of anNPN transistor Q1 comprising a portion of the relay circuit 98. Thecollector of transistor ()1 is connected to one end of the coil Ll ofthe relay the contacts of which comprise the loop cut-out switch 51, theother end of coil Ll being connected to a suitable positive supply andalso back to the collector of Q1 through a series field dischargecircuit comprising a forward polled diode D8 and a resistor R26. Whenthe net negative voltage resulting from the full wave rectification ofthe output of low pass filter 90 exceeds the low frequency roughnessthreshold established by potentiometer 96, the output of amplifier A7instantaneously rises to the breakdown voltage of Zener diode D7 therebyforward biasing transistor Q1 into conduction to energize coil L1 andopen switch S1. When the low frequency roughness thereafter subsides sothat the net negative voltage resulting from the full wave rectification of the output of low pass filter 90 is less than the lowfrequency roughness threshold provided by potentiometer 96, the outputof amplifier A7 instantaneously switches to virtual ground communicatedthereto from the inverting input through the D7 feedback loop, therebycutting off transistor Q1 and accordingly causing contacts S1 to returnto their normally closed position.

The hereinabove described cut-out sub-loop 84 is operative to modify, bydisabling, the normal operation of the lean limit loop 12 when themagnitude of those low frequency accelerations and decelerationsordinarily resulting from driver commanded changes in vehicleperformance exceed a predetermined roughness magnitude determined by thelow frequency roughness reference provided by potentiometer 96. In thismanner the cut-out sub-loop 8d permits the lean limit loop 12 tonormally control the air/fuel ratio only when the magnitude of just thehigher frequency accelerations and decelerations exceed thepredetermined roughness magnitude determined by potentiometer 73.

As may be better understood with reference to FIG. 5, the same result oflimiting the normal operation of lean limit loop 12 to the presence ofjust higher frequency accelerations and decelerations is obtained by amore simple and efficient embodiment 12. In this alternative embodiment12, the entire cut-out sub-loop 84 illustrated in FIGS. 3 and 4 isreplaced with just an additional differentiator and filter stage 73inserted between the output of the first differentiator and filter stageand the input of the full wave rectifier and comparator combinationconnected to integrator 82. The second differentiator and filter stage73 provides an output varying with the second derivative of the speedsignal applied to terminal T1 of the first differentiator and filterstage 70 and thereby permits the alternative lean limit loop 12 toanticipate the incipient roughness associated not only with large butslow engine accelerations and decelerations but also the roughnessassociated with small but fast changes in such accelerations anddecelerations. Since the roughness signal provided by the rectifier andfilter combination indicates the rate of change of acceleration anddeceleration rather than just the rate of change of speed, it thereforeis indicative of either those small changes in acceleration ordeceleraion occurring very rapidly, or in this case at high frequencies,or those large accelerations and decelerations occurring at lowerfrequencies. Lean limit loop 12 is therefore substantially moresensitive, for comparable magnitude of acceleration and deceleration, tothe roughness caused by the higher frequency components of the speedsignal such as those related to momentary differences in the powergenerated by sequentially firing cylinders than by roughness caused bylower frequency components of the speed signal such as those related todriver commanded engine performance changes. Moreover, by appropriateselection of the resistors and capacitors comprising the first andsecond differentiator and filter stages 70 and 73, the lower frequencycomponents of the second derivative signal produced by the seconddifferentiator stage are even further attenuated with respect to thelower frequency components passed by the first differentiator stage 70so as to be virtually eliminated.

To aid the understanding of the nature and operation of the units andcomponents comprising lean limit loop 12' illustrated in FIG. 5,reference should be had to the hereinabove provided descriptions ofsimilar units and components provided in conjunction with FIG. 4, suchsimilar units and components being identically designated. Thus, thefirst differentiator and filter stage 70 filters and differentiates thespeed signal provided at input terminal T1 and provides on conductor 72a derivative signal varying with the first derivative of the speedsignal. The output on conductor 72 is coupled by a capacitor C6 to theinverting input terminal of an operational amplifier A8 of the seconddifferentiator and filter stage 73, the non-inverting input terminal ofamplifier A8 being suitably grounded. The A8 output terminal iscommunicated back to the inverting input terminal by a filter circuitcomprising capacitor C7 in par allel with resistor R27, the capacitor C6and resistor R27 in combination with amplifier A8 also comprising aconventional differentiator having a lead type transfer function rs. Theoutput of the second differentiator and filter stage 73 is appliedthrough the input of the full wave rectifier and comparator combinationwhich, while illustrated as comprising a half-wave rectifier stage 92and comparator stage 94 similar to those illustrated and describedhereinabove with respect to the cut-out sub-loop 84, could also comprisea full wave rectifier 74 and comparator 76 also illustrated anddescribed hereinabove with reference to FIG. 4. Similarly, the air/fuelpre-set circuit 86 for initial conditioning the output of lean limitloop 12' performs substantially the same function as the air/fuelpre-set circuit 86 initial conditioning lean limit loop 12, circuit 86'just replacing the switch S2 in the input circuit to the invertingterminal of amplifier A4 of integrator 82 with an NPN transistor Q2 anda uni-junction transistor Q3. With the Q2 collector coupled to both asource of positive supply through a resistor R30 and to the Q3 base andwith the Q2 emitter both suitably grounded and biased by a resistor R29with respect to the Q2 base, a positive input command to theinitialization terminal T3 is communicated to the Q2 base through aresistor R28 thereby switching on transistor Q2 and in turn uni-junctionQ3. With uni-junction Q3 turned on, the voltage at the node betweenfeedback resistor R14 and potentiometer wiper arm resistor R12 iscoupled to the inverting input terminal of amplifier A4 to effect apredetermined positive output on terminal T2 such output effecting thedesired pre-set air/fuel ratio.

Based on limited data obtained from tests of the lean limit loop 12 inthe laboratory environment illustrated on FIG. 1, it was determined fromsteady state tests that good drivability could be maintained forair/fuel ratios as high as 19:1. in a standard constant volume sample(CVS) driving cycle, the lean limit loop 12 operated satisfactorily tomaintain very good driveability while at the same time significantlyreducing the mass emission of certain pollutants, hydrocarbons forexample, from a baseline value of 3.732 grams per mile at a baselineair/fuel ratio of 14.5 without the loop operative to a value of 0.756grams per mile with the loop operative to vary the air/fuel ratio from14 to 20, such ratios being calculated from actual measurements of airflow and fuel flow and such emission values being obtained from samplescollected and analyzed.

The following is a table of representative values and designations ofcomponents used that were used to construct and operate circuits of thetype illustrated in FIGS. 4 and 5.

TABLE OF COMPONENT VALUES RESISTORS (Ohms) CAPACITORS (Farads) Rl 12K c14;. R2 12R c2 2 R3 500K (:3 pm Rp68p 4 10K c4 10 R5 K cs 0.1,. R6 10K C62,. R7 10K 07 0.1,. R8 lOK R10 5K TRANSISTORS R11 lMEG.

R12 10K Q1 2N3565 R13 5K 02 2N356S R14 10K 03 2N5033 R15 1014 R16 lOOKR17 IOK R18 lOK DIODES R20 IOK o1 lN400l R21 IOK D2 D0. R22 5K D32N5230-4.7v R23 5K D4 D0. R24 10K 05 [N400] R25 10K D6 D0. R26 360 D72N52304.7v R27 560K D 8 1N4001 R28 5K D9 D0. R29 lK R 1K 6 Havingdescribed several embodiments of the invenfor the purpose of limitation.Other embodiments of the invention, modifications thereof, andalternative thereto will be obvious to those skilled in the art may bemade without departing from our invention. We therefore aim in theappended claims to cover the modifications and changes as are within thetrue scope and spirit of our invention.

What we claim is:

I. An engine control system for controlling an engine parameter of aninternal combustion engine having a variable speed member the speed ofwhich varies with the speed of the engine:

a. speed sensing means operatively associated with said variable speedmember for providing a speed signal varying with the speed thereof;

b. speed signal differentiating means operatively connected inelectrical circuit with said speed sensing means for providing a speedrate of change signal varying with a derivative of said speed signal;

0. rectifier means operatively connected in electrical circuit with saidspeed signal differentiating means 1 for rectifying said speed rate ofchange signal and providing a rectified roughness output signal;

d. comparator means connected in electrical circuit with said rectifiermeans operative to provide a comparison signal having first and secondmagnitudes when said rectified roughness output signal is respectivelyabove and below a predetermined magnitude;

e. integrator means operatively connected with said comparator meansoperative to generate a control signal having a magnitude changing at afirst predetermined rate when the magnitude of said comparison signal isone of said first and second magnitudes and at a second predeterminedrate when the magnitude of said comparison signal is the other of saidfirst and second magnitudes; and

control means operatively connected with said integrator means and saidengine responsive to control said engine parameter in accordance withsaid control signal.

2. The control system of claim 1, wherein said rectifier means comprisesa full wave rectifier and wherein said first and second predeterminedrates cause the magnitude of said control signal to respectivelyincrease and decrease.

3. An engine control system for controlling an engine parameter of aninternal combustion engine having a variable speed member the speed ofwhich varies with the speed of the engine;

a. speed sensing means operatively associated with said variable speedmember for providing a speed signal varying with the speed thereof;

b. speed signal differentiating means operatively connected inelectrical circuit with said speed sensing means for providing a speedchange signal varying with a derivative of said speed signal;

0. comparator means connected in electrical circuit with said speedsignal differentiating means operative to provide a comparison signalhaving first and second magnitudes when the magnitude of said speedchange signal is respectively above and below a predetermined magnitude;

d. integrator means operatively connected with said comparator meansoperative to generate a control I signal increasing in magnitude whenthe magnitude of said comparison signal is one of said first and secondmagnitudes and decreasing the magnitude when the magnitude of saidcomparison signal is the other of said first and second magnitudes; and

e. control means operatively connected with said integrator means andsaid engine responsive to control said engine parameter in accordancewith said control signal.

4. An engine control system for controlling an engine parameter of aninternal combustion engine having a variable speed member the speed ofwhich varies with the speed of the engine:

a. speed sensing means operatively associated with said variable speedmember for providing a speed signal varying with the speed thereof;

b. speed signal differentiating means operatively connected inelectrical circuit with said speed sensing means for providing a speedrate of change signal varying with a derivative of said speed signal;

c. rectifier means operatively connected in electrical circuit with saidspeed signal differentiating means for rectifying said speed rate ofchange signal and providing a roughness signal;

d. integrator means operatively connected with said rectifier means forgenerating a control signal varying with an integral of said roughnesssignal; and

e. control means operatively connected with said integrator means andsaid engine responsive to control said engine parameter in accordancewith said control signal.

5. An air/fuel ratio control system for an internal combustion enginehaving controllable fuel delivery means and a rotatable member rotatableat speeds varying with the speed of the engine, said air/fuel ratiocontrol system comprising:

a. speed sensor means responsively connected to the engine to provide aspeed signal varying with the speed of the rotatable member;

b. differentiator means operatively connected to said speed sensor meansfor differentiating said speed signal and providing a roughness signalvarying with a derivative of said speed signal;

0. integrator means operatively connected to said differentiator meansfor integrating said roughness signal to provide a predeterminedcorrection signal; and

d. control means operatively connected to said integrator means and tosaid fuel delivery means for varying said air/fuel ratio by controllingsaid fuel delivery means in accordance with said predeterminedcorrection signal.

6. An air/fuel ratio control system for controlling the mixture of airand fuel delivered to an internal combustion engine, the engine havingair induction means for admitting an operator controllable air flow,fuel delivery means for delivering a controllable fuel flow to the airinduction means in a controllable proportion to the air flow, and arotatable member the momentary speed changes of which vary with themomentary speed changes of the engine to indicate the roughness ofengine operation, said air/fuel control system comprising:

a. engine roughness sensing means responsively connected to the engineto sense momentary speed changes of the rotatable member and operativeto provide a roughness signal having a magnitude varying with the sensedmomentary speed changes; and

b. fuel delivery control means operatively connecting the fuel deliverymeans and the said engine roughness sensing means for controlling thefuel delivery means so as to vary the fuel flow in a preselectedrelationship to the air flow so as to maintain the magnitude of saidroughness signal at a predetermined magnitude.

7. An air/fuel ratio limit control system for limiting the leanness ofan air/fuel mixture delivered to an internal combustion engine, theengine having air induction means for admitting an operator controllableair flow, fuel delivery means for delivering a controllable fuel flow tothe air induction means, and a rotatable member the speed of whichvaries with the speed of the engine and the speed change of which varieswith the roughness of the engine and also with the magnitude of theair/fuel mixture delivered thereto, said air/fuel ratio limit controlsystem comprising:

a. engine roughness sensing means responsive to the speed changes of therotatable member to provide a roughness signal varying with theroughness of the engine; and

b. fuel delivery control means operative to normally control the fueldelivery means so as to deliver the fuel flow in a known relation to theair flow when the roughness signal is less than a predeterminedmagnitude and to otherwise cooperate with the roughness sensing means tocause the fuel delivery means to increase the fuel flow in relation tothe air flow when said roughness signal exceeds said predeterminedmagnitude, whereby the leanness of the air/fuel mixture delivered to theengine is controlled to maintain said roughness signal below saidpredetermined magnitude.

8. An air/fuel ratio control system for controlling an engineperformance related parameter of an internal combustion engine, theengine performance related parameter exceeding a predetermined magnitudeas the magnitude of the air/fuel ratio exceeds a predetermined ratio,the engine having air induction means for admitting an operatorcontrol-lable air flow, controllable fuel metering means for providing afuel flow in a controllable ratio to the air flow, and a variable speedmember the instantaneous speed changes of which vary with the magnitudeof the engine performance related parameter, said air/fuel ratio controlsystem comprising:

a. speed change sensing means operatively coupled to said engine forproviding a speed change signal varying in magnitude with the magnitudeof said instantaneous speed changes of said variable speed member;

b. control signal generation means for generating a speed change relatedcontrol signal the magnitude of which increases as the magnitude of saidspeed change signal exceeds a predetermined magnitude; and

c. fuel metering control means operatively connected to said fuelmetering means and said control signal generation means responsive tosaid speed change related control signal to normally increase theair/fuel ratio towards said predetermined ratio when the magnitude ofsaid engine performance related parameter is less than saidpredetermined magnitude and to otherwise reduce the air/fuel ratio airflow, controllable fuel metering means for varying the fuel flow in acontrollable proportion to the air flow in accordance with a speedsignal and with a speed change related signal, and a rotatable memberrotatable at speeds varying with the speed of the engine, said air/fuelratio control system comprising:

a. speed sensor means operatively connected to said control-lable fueldelivery means and to said rotatable member for generating said speedsignal varying with the speed of the rotatable member;

b. differentiator means operatively connected to said speed sensor meansfor differentiating said speed signal and providing a roughnes signalvarying with a derivative of said speed signal; and

c. signal generating means operatively connected with saiddifferentiator means and said controllable fuel delivery means forgenerating said speed change related signal in accordance with amagnitude of said roughness signal, said speed change related controlsignal operative to cause said controllable fuel delivery means toincrease the air/fuel ratio'when said roughness signal is less than apredetermined roughness magnitude and to cause said controllable fueldelivery means to decrease the air/fuel ratio when said roughness signalis greater than said predetermined roughness magnitude.

10. An air/fuel ratio control system for an internal combustion enginehaving controllable fuel delivery means for varying the air/fuel ratioin accordance with a speed signal and the speed change related signal, arotatable member rotatable at speeds varying with the speed of theengine, and speed sensor means responsively associated with saidrotatable member for generating said speed signal for said controllablefuel delivery means, said speed signal having low frequency componentsindicative of low frequency driver commanded performance changes andhigher frequency components varying with the magnitude of an engineperformance related parameter, said air/fuel ratio control systemcomprising:

a. differentiator means operatively connected to said speed sensor meansfor differentiating said speed signal and providing a roughness signalvarying with a derivative of at least said higher frequency componentsof said speed signal;

b. control means operatively connected to said differentiator means forgenerating said speed change related control signal in accordance withthe magnitude of said roughness signal, said speed change relatedcontrol signal causing said controllable fuel delivery means to increasesaid air/fuel ratio when said roughness signal is below a predeterminedroughness magnitude and to decrease said air/fuel ratio when themagnitude of said roughness signal is above said predetermined roughnessmagnitude.

11. In the apparatus of claim 10, said derivative of said speed signalbeing the second derivative thereof whereby the magnitude of theresulting roughness signal varies with the magnitude of just said higherfrequency components of the speed signal so that the speed changerelated signal does not cause the fuel delivery means to decrease theair/fuel ratio in the presence of said low frequency driver commandedperformance changes.

12. In the apparatus of claim 10, said control means including frequencysensitive control override means responsive to said low frequencycomponents to prevent said speed change related signals from causingsaid fuel delivery means to decrease the air/fuel ratio in the presenceof said low frequency driver commanded performance changes.

13. An air/fuel ratio control system for an internal combustion enginehaving controllable fuel delivery means and a rotatable member rotatableat speeds varying with the speed of the engine, said air/fuel ratiocontrol system comprising:

a. speed sensor means responsively connected to the engine to providethe speed signal varying with the speed of the rotatable member, saidspeed signal having low and high frequency components;

b. differentiator means operatively connected to said speed sensor meansfor differentiating said speed signal and providing a roughness signalvarying with a derivative of said high frequency component of said speedsignal;

c. first control means operatively connecting said differentiator meansand said controllable fuel delivery means causing said fuel deliverymeans to increase the air/fuelratio when said roughness signal is lessthan a predetermined roughness magnitude, and to decrease said air/fuelratio when the magnitude of said roughness signal is greater than saidpredetermined roughness magnitude; and

d. second control means operatively connected between said first controlmeans and said differentiator means for modifying said speed changerelated signal when the magnitude of said low frequency componentsexceeds a predetermined low frequency magnitude.

14. A roughness control system for controlling the roughness of aninternal combustion engine, the engine having an operator controllableair fuel delivery means for delivering a controllable air fuel mixtureand a rotatable member the momentary speed changes of which vary withthe momentary speed changes of the engine to indicate the roughness ofengine operation, said roughness control system comprising:

a. engine roughness sensing means responsively connected to the enginefor sensing momentary speed changes of the rotatable member andproviding a roughness signal having a magnitude varying with the sensedmomentary speed changes; and

b. control means operatively connecting the air fuel delivery means andthe said engine roughness sensing means for controlling the air fueldelivery means so as to regulate the magnitude of said roughness signalat a predetermined magnitude.

15. An air/fuel ratio control system for controlling the mixture of airand fuel delivered to an internal combustion engine, the engine havingan operator controllable air fuel delivery means for delivering avariable ratio air fuel mixture and a rotatable member and modeliverymeans and the said engine roughness sensing means for controlling thefuel delivery means so as to normally bias the air fuel ratio in a leandirec tion until the magnitude of said roughness signal exceeds apredetermined magnitude and to thereafter decrease the air fuel ratio ina rich direction, whereby the air fuel delivery means regulates themagnitude of said roughness signal at said predetermined magnitude.

I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,7895 Dated February 5 I974 Inventofls) Lael. ,B. Taplin William R. Sei t2and Chun Keunq Leunq It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In column l line 4l the word should be "ineffectual" instead of"effectual In column 3 line 3l "as lean as" should be corrected to read"as lean an";

In column 7, line 22, the word should be "transmissions" instead of 7"transmission".

In column 9, lin30, after the word "described" insert as follows '---anddescribed more specifically in commonly-assigned United States patentapplication 289,200 filed September l4, l972 by William R. Seitz andentitled Closed Loop Engine Control System," such application beingexpressly incorporated herein by reference.--

In column 10, line 42, before the 'word "drop" insert the word"yoltage".

In column 12, line 17, "deceleraion" should read "deceleration".

In column 13, line44 "Rp68p 4" should be "R4".

In column 16 line 43 Claim 8, change "control -lable" to---controllable- In column l7, line 18, Claim 9 change "control-lable"to ---controllable-v--.

In column 18, line 67 Claim l5, change member and" to ---member the---.

' Signed and sealed this 16th day of July 1971 YQ(SEAL). I. I

Attest:

McCOY M. GIBSON, JR.- c. MARSHALL DANN Attesting Bffioer Commissioner ofPatents FORM PC4050 (10-69) uscoMM-oc 60376-P69 I i W U454 GOVIINIIINFill UNIS OFFICE I I". 0-365-334 v

1. An engine control system for controlling an engine parameter of aninternal combustion engine having a variable speed member the speed ofwhich varies with the speed of the engine: a. speed sensing meansoperatively associated with said variable speed member for providing aspeed signal varying with the speed thereof; b. speed signaldifferentiating means operatively connected in electrical circuit withsaid speed sensing means for providing a speed rate of change signalvarying with a derivative of said speed signal; c. rectifier meansoperatively connected in electrical circuit with said speed signaldifferentiating means for rectifying said speed rate of change signaland providing a rectified roughness output signal; d. comparator meansconnected in electrical circuit with said rectifier means operative toprovide a comparison signal having first and second magnitudes when saidrectified roughness output signal is respectively above and below apredetermined magnitude; e. integrator means operatively connected withsaid comparator means operative to generate a control signal having amagnitude changing at a first predetermined rate when the magnitude ofsaid comparison signal is one of said first and second magnitudes and ata second predetermined rate when the magnitude of said comparison signalis the other of said first and second magnitudes; and f. control meansoperatively connected with said integrator means and said engineresponsive to control said engine parameter in accordance with saidcontrol signal.
 2. The control system of claim 1, wherein said rectifiermeans comprises a full wave rectifier and wherein said first and secondpredetermined rates cause the magnitude of said control signal torespectively increase and decrease.
 3. An engine control system forcontrolling an engine parameter of an internal combustion engine havinga variable speed member the speed of which varies with the speed of theengine; a. speed sensing means operatively associated with said variablespeed member for providing a speed signal varying with the speedthereof; b. speed signal differentiating means operatively connected inelectrical circuit with said speed sensing means for providing a speedchange signal varying with a derivative of said speed signal; c.comparator means connected in electrical circuit with said speed signaldifferentiating means operative to provide a comparison signal havingfirst and second magnitudes when the magnitude of said speed changesignal is respectively above and below a predetermined magnitude; d.integrator means operatively connected with said comparator meansoperative to generate a control signal increasing in magnitude when themagnitude of said comparison signal is one of said first and secondmagnitudes and decreasing the magnitude when the magnitude of saidcomparison signal is the other of said first and second magnitudes; ande. control means operatively connected with said integrator means andsaid engine responsive to control said engine parameter in accordancewith said control signal.
 4. An engine control system for controlling anengine parameter of an internal combustion engine having a variablespeed member the speed of which varies with the speed of the engine: a.speed sensing means operatively associated with said variable speedmember for providing a speed signal varying with the speed thereof; b.speed signal differentiating means operatively connected in electricalcircuit with said speed sensing means for providing a speed rate ofchange signal varying with a derivative of said speed signal; c.rectifier means operatively connected in electrical circuit with saidspeed signal differentiating means for rectifying said speed rate ofchange signal and providing a roughness signal; d. integrator meansoperatively connected with said rectifier means for generating a controlsignal varying with an integral of said roughness signal; and e. controlmeans operatively connected with said integrator means and said engineresponsive to control said engine parameter in accordance with saidcontrol signal.
 5. An air/fuel ratio control system for an internalcombustion engine having controllable fuel delivery means and arotatable member rotatable at speeds varying with the speed of theengine, said air/fuel ratio control system comprising: a. speed sensormeans responsively connected to The engine to provide a speed signalvarying with the speed of the rotatable member; b. differentiator meansoperatively connected to said speed sensor means for differentiatingsaid speed signal and providing a roughness signal varying with aderivative of said speed signal; c. integrator means operativelyconnected to said differentiator means for integrating said roughnesssignal to provide a predetermined correction signal; and d. controlmeans operatively connected to said integrator means and to said fueldelivery means for varying said air/fuel ratio by controlling said fueldelivery means in accordance with said predetermined correction signal.6. An air/fuel ratio control system for controlling the mixture of airand fuel delivered to an internal combustion engine, the engine havingair induction means for admitting an operator controllable air flow,fuel delivery means for delivering a controllable fuel flow to the airinduction means in a controllable proportion to the air flow, and arotatable member the momentary speed changes of which vary with themomentary speed changes of the engine to indicate the roughness ofengine operation, said air/fuel control system comprising: a. engineroughness sensing means responsively connected to the engine to sensemomentary speed changes of the rotatable member and operative to providea roughness signal having a magnitude varying with the sensed momentaryspeed changes; and b. fuel delivery control means operatively connectingthe fuel delivery means and the said engine roughness sensing means forcontrolling the fuel delivery means so as to vary the fuel flow in apreselected relationship to the air flow so as to maintain the magnitudeof said roughness signal at a predetermined magnitude.
 7. An air/fuelratio limit control system for limiting the leanness of an air/fuelmixture delivered to an internal combustion engine, the engine havingair induction means for admitting an operator controllable air flow,fuel delivery means for delivering a controllable fuel flow to the airinduction means, and a rotatable member the speed of which varies withthe speed of the engine and the speed change of which varies with theroughness of the engine and also with the magnitude of the air/fuelmixture delivered thereto, said air/fuel ratio limit control systemcomprising: a. engine roughness sensing means responsive to the speedchanges of the rotatable member to provide a roughness signal varyingwith the roughness of the engine; and b. fuel delivery control meansoperative to normally control the fuel delivery means so as to deliverthe fuel flow in a known relation to the air flow when the roughnesssignal is less than a predetermined magnitude and to otherwise cooperatewith the roughness sensing means to cause the fuel delivery means toincrease the fuel flow in relation to the air flow when said roughnesssignal exceeds said predetermined magnitude, whereby the leanness of theair/fuel mixture delivered to the engine is controlled to maintain saidroughness signal below said predetermined magnitude.
 8. An air/fuelratio control system for controlling an engine performance relatedparameter of an internal combustion engine, the engine performancerelated parameter exceeding a predetermined magnitude as the magnitudeof the air/fuel ratio exceeds a predetermined ratio, the engine havingair induction means for admitting an operator control-lable air flow,controllable fuel metering means for providing a fuel flow in acontrollable ratio to the air flow, and a variable speed member theinstantaneous speed changes of which vary with the magnitude of theengine performance related parameter, said air/fuel ratio control systemcomprising: a. speed change sensing means operatively coupled to saidengine for providing a speed change signal varying in magnitude with themagnitude of said instantaneous speed changes of said variable speedmember; b. control signal generation means for Generating a speed changerelated control signal the magnitude of which increases as the magnitudeof said speed change signal exceeds a predetermined magnitude; and c.fuel metering control means operatively connected to said fuel meteringmeans and said control signal generation means responsive to said speedchange related control signal to normally increase the air/fuel ratiotowards said predetermined ratio when the magnitude of said engineperformance related parameter is less than said predetermined magnitudeand to otherwise reduce the air/fuel ratio when the magnitude of saidengine performance related parameter exceeds said magnitude, whereby themagnitudes of said air/fuel ratio and said engine performance relatedparameter are continually varied at magnitudes less than saidpredetermined ratio and predetermined magnitude.
 9. An air/fuel ratiocontrol system for an internal combustion engine having a rotatablemember rotatable at speeds varying with the speed of the engine, airinduction means for admitting an operator controllable air flow,controllable fuel metering means for varying the fuel flow in acontrollable proportion to the air flow in accordance with a speedsignal and with a speed change related signal, and a rotatable memberrotatable at speeds varying with the speed of the engine, said air/fuelratio control system comprising: a. speed sensor means operativelyconnected to said control-lable fuel delivery means and to saidrotatable member for generating said speed signal varying with the speedof the rotatable member; b. differentiator means operatively connectedto said speed sensor means for differentiating said speed signal andproviding a roughnes signal varying with a derivative of said speedsignal; and c. signal generating means operatively connected with saiddifferentiator means and said controllable fuel delivery means forgenerating said speed change related signal in accordance with amagnitude of said roughness signal, said speed change related controlsignal operative to cause said controllable fuel delivery means toincrease the air/fuel ratio when said roughness signal is less than apredetermined roughness magnitude and to cause said controllable fueldelivery means to decrease the air/fuel ratio when said roughness signalis greater than said predetermined roughness magnitude.
 10. An air/fuelratio control system for an internal combustion engine havingcontrollable fuel delivery means for varying the air/fuel ratio inaccordance with a speed signal and the speed change related signal, arotatable member rotatable at speeds varying with the speed of theengine, and speed sensor means responsively associated with saidrotatable member for generating said speed signal for said controllablefuel delivery means, said speed signal having low frequency componentsindicative of low frequency driver commanded performance changes andhigher frequency components varying with the magnitude of an engineperformance related parameter, said air/fuel ratio control systemcomprising: a. differentiator means operatively connected to said speedsensor means for differentiating said speed signal and providing aroughness signal varying with a derivative of at least said higherfrequency components of said speed signal; b. control means operativelyconnected to said differentiator means for generating said speed changerelated control signal in accordance with the magnitude of saidroughness signal, said speed change related control signal causing saidcontrollable fuel delivery means to increase said air/fuel ratio whensaid roughness signal is below a predetermined roughness magnitude andto decrease said air/fuel ratio when the magnitude of said roughnesssignal is above said predetermined roughness magnitude.
 11. In theapparatus of claim 10, said derivative of said speed signal being thesecond derivative thereof whereby the magnitude of the resultingroughness signal varies with the magnitude of just said Higher frequencycomponents of the speed signal so that the speed change related signaldoes not cause the fuel delivery means to decrease the air/fuel ratio inthe presence of said low frequency driver commanded performance changes.12. In the apparatus of claim 10, said control means including frequencysensitive control override means responsive to said low frequencycomponents to prevent said speed change related signals from causingsaid fuel delivery means to decrease the air/fuel ratio in the presenceof said low frequency driver commanded performance changes.
 13. Anair/fuel ratio control system for an internal combustion engine havingcontrollable fuel delivery means and a rotatable member rotatable atspeeds varying with the speed of the engine, said air/fuel ratio controlsystem comprising: a. speed sensor means responsively connected to theengine to provide the speed signal varying with the speed of therotatable member, said speed signal having low and high frequencycomponents; b. differentiator means operatively connected to said speedsensor means for differentiating said speed signal and providing aroughness signal varying with a derivative of said high frequencycomponent of said speed signal; c. first control means operativelyconnecting said differentiator means and said controllable fuel deliverymeans causing said fuel delivery means to increase the air/fuel ratiowhen said roughness signal is less than a predetermined roughnessmagnitude and to decrease said air/fuel ratio when the magnitude of saidroughness signal is greater than said predetermined roughness magnitude;and d. second control means operatively connected between said firstcontrol means and said differentiator means for modifying said speedchange related signal when the magnitude of said low frequencycomponents exceeds a predetermined low frequency magnitude.
 14. Aroughness control system for controlling the roughness of an internalcombustion engine, the engine having an operator controllable air fueldelivery means for delivering a controllable air fuel mixture and arotatable member the momentary speed changes of which vary with themomentary speed changes of the engine to indicate the roughness ofengine operation, said roughness control system comprising: a. engineroughness sensing means responsively connected to the engine for sensingmomentary speed changes of the rotatable member and providing aroughness signal having a magnitude varying with the sensed momentaryspeed changes; and b. control means operatively connecting the air fueldelivery means and the said engine roughness sensing means forcontrolling the air fuel delivery means so as to regulate the magnitudeof said roughness signal at a predetermined magnitude.
 15. An air/fuelratio control system for controlling the mixture of air and fueldelivered to an internal combustion engine, the engine having anoperator controllable air fuel delivery means for delivering a variableratio air fuel mixture and a rotatable member and momentary speedchanges of which vary with the momentary speed changes of the engine toindicate the roughness of engine operation, said air/fuel control systemcomprising: a. engine roughness sensing means responsively connected tothe engine for sensing momentary speed changes of the rotatable memberand providing a roughness signal having a magnitude varying with thesensed momentary speed changes; and b. control means operativelyconnecting the air fuel delivery means and the said engine roughnesssensing means for controlling the fuel delivery means so as to normallybias the air fuel ratio in a lean direction until the magnitude of saidroughness signal exceeds a predetermined magnitude and to thereafterdecrease the air fuel ratio in a rich direction, whereby the air fueldelivery means regulates the magnitude of said roughness signal at saidpredetermined magnitude.